/*]
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef AAPT_WORK_QUEUE_H
#define AAPT_WORK_QUEUE_H

#include <utils/Errors.h>
#include <utils/Vector.h>
#include <utils/threads.h>

namespace android {

/*
 * A threaded work queue.
 *
 * This class is designed to make it easy to run a bunch of isolated work
 * units in parallel, using up to the specified number of threads.
 * To use it, write a loop to post work units to the work queue, then synchronize
 * on the queue at the end.
 */
    class WorkQueue {
    public:
        class WorkUnit {
        public:
            WorkUnit() {}

            virtual ~WorkUnit() {}

            /*
             * Runs the work unit.
             * If the result is 'true' then the work queue continues scheduling work as usual.
             * If the result is 'false' then the work queue is canceled.
             */
            virtual bool run() = 0;
        };

        /* Creates a work queue with the specified maximum number of work threads. */
        explicit WorkQueue(size_t maxThreads, bool canCallJava = true);

        /* Destroys the work queue.
         * Cancels pending work and waits for all remaining threads to complete.
         */
        ~WorkQueue();

        /* Posts a work unit to run later.
         * If the work queue has been canceled or is already finished, returns INVALID_OPERATION
         * and does not take ownership of the work unit (caller must destroy it itself).
         * Otherwise, returns OK and takes ownership of the work unit (the work queue will
         * destroy it automatically).
         *
         * For flow control, this method blocks when the size of the pending work queue is more
         * 'backlog' times the number of threads.  This condition reduces the rate of entry into
         * the pending work queue and prevents it from growing much more rapidly than the
         * work threads can actually handle.
         *
         * If 'backlog' is 0, then no throttle is applied.
         */
        status_t schedule(WorkUnit *workUnit, size_t backlog = 2);

        /* Cancels all pending work.
         * If the work queue is already finished, returns INVALID_OPERATION.
         * If the work queue is already canceled, returns OK and does nothing else.
         * Otherwise, returns OK, discards all pending work units and prevents additional
         * work units from being scheduled.
         *
         * Call finish() after cancel() to wait for all remaining work to complete.
         */
        status_t cancel();

        /* Waits for all work to complete.
         * If the work queue is already finished, returns INVALID_OPERATION.
         * Otherwise, waits for all work to complete and returns OK.
         */
        status_t finish();

    private:
        class WorkThread : public Thread {
        public:
            WorkThread(WorkQueue *workQueue, bool canCallJava);

            virtual ~WorkThread();

        private:
            virtual bool threadLoop();

            WorkQueue *const mWorkQueue;
        };

        status_t cancelLocked();

        bool threadLoop(); // called from each work thread

        const size_t mMaxThreads;
        const bool mCanCallJava;

        Mutex mLock;
        Condition mWorkChangedCondition;
        Condition mWorkDequeuedCondition;

        bool mCanceled;
        bool mFinished;
        size_t mIdleThreads;
        Vector<sp<WorkThread> > mWorkThreads;
        Vector<WorkUnit *> mWorkUnits;
    };

}; // namespace android

#endif // AAPT_WORK_QUEUE_H
